Using regular expressions in JavaScript

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Regular expressions in Javascript are represented by a RegExp object. There also is a regex literal as in many other languages: /regex/. However, they are used slightly differently.

Regex literal

  • Usage: /foo+/
  • Shorthand for creating a regular expression object

RegExp() object

  • Usage: RegExp("foo+") or new RegExp("foo+")
  • No surrounding slashes required (they're the literal markers)
  • Since the argument is a string, backslashes need to be escaped as well: RegExp("\\d+")


matcher = new RegExp("foo", "g") // <- "global" flag
matcher.test("foobar") // => true
matcher.lastIndex // => 3 (where the regexp stopped scanning)
matcher.test("foobar") // => false
matcher.lastIndex // => 0

This does not happen when creating a new regex object each run, as with /foo/g.test("foobar"). Use String#match() if you want an array of matches.

Dominik Schöler
Last edit
Michael Leimstädtner
Source code in this card is licensed under the MIT License.
Posted by Dominik Schöler to makandra dev (2015-12-07 07:31)